Problems storing data in iPhone SQLite help!

I just started looking into SQLite for the iPhone 开发者_StackOverflowSDK. I have been looking at this tutorial and I am wondering how can I find an ID and store the information in that field of the ID? (the tutorial increments an ID every time I press save).

Also, how can I loop though the whole database e.g., add all the id numbers up? Is there a command?

Not much changes in the database access in the methods. Only the SQLite query changes. It should be something on these lines.

- (NSInteger) sumOfIds
{
    const char    *dbpath = [databasePath UTF8String];
    sqlite3_stmt  *statement;
    NSString      *result;

    if (sqlite3_open(dbpath, &contactDB) == SQLITE_OK)
    {
        NSString *querySQL = @"SELECT sum(id) FROM contacts";
        const char *query_stmt = [querySQL UTF8String];

        if (sqlite3_prepare_v2(contactDB, query_stmt, -1, &statement, NULL) == SQLITE_OK)
        {
            if (sqlite3_step(statement) == SQLITE_ROW)
            {
                NSString *result = [[NSString alloc] initWithUTF8String:(const char *)sqlite3_column_text(statement, 0)];
            }
            sqlite3_finalize(statement);
        }
        sqlite3_close(contactDB);
    }

    return [result floatValue];
}